The Fujifilm GFX facebook group is very active, and those interested to know about it, make well to follow it. You’ll find the GFX tidbits there faster then I can share them here on FujiRumors.
Some of the group seem to have also access to the interesting backstage, where a selected group of people can actually hold working protoypes. One of them is Max Angeloni (riflessifotografici), and he shared on the group this video. His comment
“So … the Fujifilm GFX is still under development. So even the specifications have not all been revealed. Official data can be read on the brochure. For the rest we have to wait a bit ‘ . Surely already now it appears going in the right way regarding operating speed“
I’ve uploaded the video on my youtube channel, in order to make it visible to everybody, also those, who don’t have facebook and do not want to join the group. But the original content can be found here.
If you have any questions, talk directly to Max in this facebook post.
UPDATE: According to mirrorlessons here, the Fujifilm GFX should have a native ISO that starts from 100.